Production of metal strip from metal powder

ABSTRACT

IN THE ROLL COMPACTION OF METAL POWDER TO FORM METAL STRIP THE POWDER IS SUPPLIED TO THE ROLL NIP BY MEANS OF A HOPPER. THE END WALLS OF THE HOPPER HAVE A CENTRAL POROUS AREA THROUGH WHICH GAS CAN BE PASSED. THIS PREVENTS THE POWDER STICKING TO THE END WALLS. THUS, POWDER CAN BE FED UNIFORMLY TO THE ROLL NIP SO THAT STRIP OF CONSTANT WEIGHT PER UNIT AREA ACROSS ITS WIDTH CAN BE PRODUCED.

y 4, 1972 G. MQHARDY STURGEON ET AL 3,674,390

PRODUCTION OF METAL STRIP FROM METAL POWDER Filed July 27, 1970 IN VE N TOPS 6502 5 MO/MRDY STt/RG-EON 6502 5 Jim/(50M A T TOPNEYS United States Patent Office 3,674,390 Patented July 4, 1972 3,674,390 PRODUCTION OF METAL STRIP FROM METAL POWDER George McHardy Sturgeon, Sheflield, and George Jackson, Dronfield Woodhouse, near Sheffield, England, assignors to The British Iron and Steel Research Association, London, England Filed July 2 7, 1970, Ser. No. 58,587 Claims priority, application Great Britain, Aug. 6, 1969, 39,328/ 69 Int. Cl. B29d 7/14 U.S. Cl. 425-79 4 Claims ABSTRACT OF THE DISCLOSURE In the roll compaction of metal powder to form metal strip the powder is supplied to the roll nip by means of a hopper. The end walls of the hopper have a central porous area through which gas can be passed. This prevents the powder sticking to the end walls. Thus, powder can be fed uniformly to the roll nip so that strip of constant weight per unit area across its width can be produced.

This invention relates to the production of metal strip by the compaction of metal powder.

Metal powders can be formed into strip material by supplying the powder to the nip of compacting rolls where the powder is subjected to sufiicient pressure to form a self-supporting strip (commonly termed green strip) and subsequently heating the strip to sinter the metal particles. Thereafter the sintered metal strip may be subjected to mechanical and/or thermal treatment to modify and, in particular, to improve its mechanical properties.

Alternatively, hot metal powder may be supplied to the roll nip so that thermal treatment occurs simultaneously with compaction.

In carrying out this process, several methods can be used to meter the powder into the roll nip. One method is to maintain a heap of powder above the nip of the compacting rolls (the powder flowing into the roll nip assisted by the rotation of the rolls) by means of a hopper which may be defined by two longitudinal walls lying parallel to the axis of the rolls, the lower edges of which bear against the curved surface of the rolls, and two end walls lying transverse to the axis of the rolls, the lower ends of which bear against the ends of the rolls. The enclosure and the upper parts of the curved surfaces of the compacting rolls form, in effect, a hopper for the powder. The powder is generally supplied to the hopper by a mechanical conveyor or pneumatically.

One of the main problems in producing satisfactory green strip for further processing into cold rolled strip is to ensure that the mass per unit area across its width is constant and it is an object of this invention to reduce this problem.

Accordingly, the present invention comprises an apparatus for use in the production of metal strip from metal powder including compacting rolls, a hopper for directing powder to the nip between the rolls, characterised in that the hopper has end walls (i.e. Walls transverse to the rolls) with means for forming a layer of pressurised gas on the inside of the end walls whereby to reduce the friction between the end walls and powder in the hopper.

Preferably, the hopper end walls include a portion of porous material through which gas can be passed.

The present invention also comprises a process for the production of metal strip from metal powder in which metal powder is supplied to the nip of compacting rolls from a hopper, characterised in that a layer of pressurised gas is formed on the inside of the end walls (i.e. walls transverse to the rolls) of the hopper to reduce the friction between the end walls and powder in the hopper.

We have found that with our invention, the friction between the hopper end walls and the powder can be reduced and that strip with improved uniformity of mass per unit area across the strip width can now be produced.

In the accompanying drawings:

FIG. 1 is a perspective view of one embodiment of apparatus according to the invention.

FIG. 2 is an elevation of one end wall of the hopper seen from inside the hopper, and

FIG. 3 is a part view of section lII--III (see FIG. 2) across the hopper.

The apparatus comprises a pair or horizontally disposed, parallel, compacting rolls 10 and 11 which are driven by means (not shown) in the directions indicated by the arrows. Superimposed on the rolls 10, 1.1 is a hopper 12 made up of two longitudinal walls 13, 14, the lower edges of which bear against the curved surfaces of the rolls 10, 1 1 respectively and two end walls 15, 16, the end wall 15 being broken away in FIG. 1, the lower ends of which bear against the ends of the rolls 10, 11 (see FIGS. 2 and 3). Positioned above the hopper 12 is a container 17 for a fluidised bed of metal powder; the bottom of the container is provided with an inlet 18, for gas to maintain the bed in a fluidised condition. One side, 19, of the container 17 is positioned vertically above and parallel to the nip formed between the rolls 10 and 11 and extends over the length of the nip; side 19 forms a weir over which the fluidised metal powder can flow and then fall into the hopper as more fully described in our application Ser. No. 58,586, filed July 27, 1970.

As shown in FIGS. 2 and 3 the end wall 16 (the end wall 15 being exactly similar) comprises a central portion 22 formed of a porous or foraminous material. Suitable materials include, for example, porous ceramic materials, porous sintered metal sheet and metal sheet having a large number of small holes in it. The central portion '22 is covered on the outside (that is on the outside relative to the hopper) by a gas-tight jacket 25 which is provided with a gas inlet 26. The bottom portion 27 of the wall, i.e. that portion adjacent the roll nip, is preferably formed solid.

In operation, metal powder is supplied to the container 17 and flows over the weir 19 into the hopper 12. Gas, for example air, is passed via the gas inlets 26 to the porous part ofthe hopper end walls 22 and forms a gaseous cushion on the inside of the hopper end walls 15, 16 thereby reducing the tendency of the powder to stick to the hopper end walls. The powder thus flows into the end portions of the nip at the same rate as into the rest of the nip and then compacted to form a strip.

The powder compacting processes and apparatus of the invention can be used in the compaction of cold powder to form green strip and also in the compaction of hot powder.

We claim:

1. In apparatus for use in the production of metal strip from metal powder including compacting rolls and a hopper for directing powder to the nip between the rolls, the improvement in which comprises hopper end walls transverse to the rolls having means for forming a layer of pressurised gas on the inside of the end walls where by to reduce the friction between the end walls and powder in the hopper.

3 4 2. Apparatps as claimed in claim 1 in which each end. 7 3,389,430 6/1968. Gehring et al. 18-9 wall includes a portion of porous material. 2,844,489 7/1958 Gemmer 18-DIG 20 3. Apparatus as claimed in claim 2 in which the bottom portion of each end wall is of solid material. FOREIGN PATENTS 4. Apparatus as claimed in claim 2 in which a gas- 5 236,261 1959 Australia 20 tight jacket is provided on the exterior of each hopper end wall with one or more gas inlets provided to the fi ht jackets J. SPENCER OV-ERHOLSER, Primary Examiner References Cited D. S. SAFRAN, Assistant Examiner UNITED STATES PATENTS 2,882,554 4/1969 Heck 42s -79 2,987,778 6/1961 Worn 264111 2641 

